Thread group and lifeccycle management (#344)

* Refreshed branch sync

* relax test

* Relax text for slow machine

.gitignore

@@ -45,3 +45,4 @@ build
 
 # CLion
 .idea
+cmake-build-*

CMakeLists.txt

@@ -16,6 +16,7 @@ dmlccore_option(USE_HDFS "Build with HDFS support" OFF)
 dmlccore_option(USE_AZURE "Build with AZURE support" OFF)
 dmlccore_option(USE_S3 "Build with S3 support" OFF)
 dmlccore_option(USE_OPENMP "Build with OpenMP" ON)
+dmlccore_option(USE_CXX14_IF_AVAILABLE "Build with C++14 if the compiler supports it" OFF)
 
 # include path
 include_directories("include")
@@ -73,7 +74,10 @@ if(MSVC)
 else(MSVC)
   set(CMAKE_POSITION_INDEPENDENT_CODE ON)
   include(CheckCXXCompilerFlag)
-  check_cxx_compiler_flag("-std=c++11"   SUPPORT_CXX11)
+  if(USE_CXX14_IF_AVAILABLE)
+    check_cxx_compiler_flag("-std=c++14"    SUPPORT_CXX14)
+  endif()
+  check_cxx_compiler_flag("-std=c++11"    SUPPORT_CXX11)
   check_cxx_compiler_flag("-std=c++0x"    SUPPORT_CXX0X)
   check_cxx_compiler_flag("-msse2"        SUPPORT_MSSE2)
   set(CMAKE_C_FLAGS "-Wall -Wno-unknown-pragmas -fPIC")
@@ -84,11 +88,18 @@ else(MSVC)
   else()
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O3")
   endif()
+  if(SUPPORT_CXX0X)
+  	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c++0x")
+  endif()
   if(SUPPORT_MSSE2)
   	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -msse2")
   endif()
   set(CMAKE_CXX_FLAGS ${CMAKE_C_FLAGS})
-  if(SUPPORT_CXX11)
+  if(SUPPORT_CXX14)
+    add_definitions(-DDMLC_USE_CXX14=1)
+    add_definitions(-DDMLC_USE_CXX11=1)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
+  elseif(SUPPORT_CXX11)
     add_definitions(-DDMLC_USE_CXX11=1)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
   elseif(SUPPORT_CXX0X)